I have tried to keep my head down like Federer as well on the forehand and backhand but it does for me at least seem awkward on the forehand. Doing it on the backhand helps but I tend to hit the ball out or in the net if I do it on the forehand.

watch contact point, i try to read the print on the ball before to keep eye contact. i like to think to keep my eyes and head there until i am able to spit after my arm has passed my head point. (i dont really spit just a reference)